Dr. Kelly Weidenbach Executive Director
Casper -Natrona County Health Department 475 South Spruce Street
Casper, Wyoming 82601
Dear Dr. Weidenbach:
On June 27, 2016, the Agency for Toxic Substances and Disease Registry (ATSDR) received an email from you regarding results of indoor air sampling at the Midwest School in Natrona, Wyoming. You requested that ATSDR review results provided by CS Consulting on behalf of Fleur de Lis Energy (FDL), and provide an analysis of the potential public health implications of exposure to gases intruding into the school from the Salt Creek oil well field. We understand that carbon dioxide (CO2) is used to pressurize the surrounding wells and on May 24, 2016, the school was evacuated because of elevated air levels of CO2. On May 26, the air levels in the building measured by FDL exceeded ATSDR short term (acute) health guidelines for benzene and the CO2 levels exceeded recommended indoor CO2 levels of 1,000 parts per million for a healthy school environment (EPA 2009). The data demonstrated a positive correlation between interior VOC concentrations and CO2 levels.
ATSDR received air sampling data from the Casper -Natrona County Health Department that documented air sampling on June 16-17, 2016. This sampling estimated average indoor air concentrations of volatile organic chemicals (VOC) and other gases in the school over an 8-hour period. Based on an evaluation of the data from the June sampling event, ATSDR determined that there were no exceedances of health-based air concentration guidelines at that time. However, it should be noted that CO2 levels were low during the June sampling period, demonstrating that the indoor air environment was different from those of the May sampling event and might not be representative of conditions when oil field operations adversely impacted building indoor air.
Conditions of operation vary and air data are not available for all circumstances when well field operations may be impacting the school. Consequently, ATSDR cannot conclude that the occupants of the school will besafe under all conditions of well field operation. It is possible that another event similar to the May 24th incident could occur in the future. ATSDR concluded that the events in May posed an urgent health hazard. ATSDR recommends that interim and more permanent mitigation be instituted before deciding to reoccupy the building in order to protect the students and staff of
Midwest School. We understand that FDL is in the process of taking corrective action to mitigate impacts to the school from oil well field operations. These actions include sealing any abandoned wells near to the school, installing soil vapor extraction under the school foundation, and conducting a comprehensive evaluation of well bores drilled within a half-mile of the school. Additionally, FDL is working with county and town officials to provide additional gas monitoring in the community adjacent to the school and oil field.
It is unclear to ATSDR whether actions taken by FDL will adequately mitigate vapor intrusion into the school building. ATSDR recommends that multiple lines of evidence be considered by the school district before reoccupying the school. This may include multiple rounds of indoor air samples and soil gas measurements under the building foundation. Additionally, ATSDR recommends that if the school is reoccupied, ongoing monitoring for volatile organic compounds and CO2 occur to ensure the continued safety of the students and staff. A safety plan should be developed in case of malfunction of the mitigation systems.
Sampling during May 26, 2016, also revealed that the air in the crawlspace under the swimming pool had elevated CO2 and voe concentrations. It is possible that this crawlspace could present a confined
space hazard to someone entering the area without adequate ventilation or protective equipment if the air in the crawlspace is oxygen deficient or voe concentrations are acutely toxic and immediately dangerous to life and health. ATSDR recommends that access to the crawlspace should be restricted and warnings placed on the crawlspace access until the situation is corrected and monitoring demonstrates that the area can be entered safely.
ATSDR understands that there are areas where gas is seeping out of the ground near the track. We understand that school district officials have notified school staff that those areas should be avoided. ATSDR recommends that access to those areas be restricted and signs be posted to avoid access to those areas until the seeps are mitigated.
A description of the evaluation of the air data is provided as an attachment to this letter, along with more detailed conclusions and recommendations. ATSDR remains available to assist with health and safety concerns. Please contact the ATSDR Denver regional office at 303-312-7012 if you have any questions regarding this letter or need further assistance.
Scott Sudweeks Regional Toxicologist
Agency for Toxic Substances and Disease Registry Centers for Disease Control and Prevention, Denver, CO
cc: Natrona County School district, WY DEQ, WY DOH